The present invention relates to a piezoelectric/electrostrictive device comprising a movable portion being operated based on a displacement of a piezoelectric/electrostrictive element, or to a piezoelectric/electrostrictive device capable of detecting a displacement of a movable portion by a piezoelectric/electrostrictive element, and more particularly relates to a piezoelectric/electrostrictive device which is superior in mechanical strength, impact resistance, and humidity resistance, and capable of having the movable portion efficiently operated with large magnitude substantially in parallel toward the direction of a specific axis.
In recent years, in the fields of optics, magnetic recording, precision machining, and the like, a displacement element capable of adjusting an optical path length or a position in sub-micron order has been required, and development has been progressed of a displacement element utilizing a displacement due to the inverse piezoelectric effect or the electrostrictive effect caused when a voltage is applied to a piezoelectric/electrostrictive material (for example, a ferroelectric substance or the like). For example, as shown in FIG. 27, a piezoelectric actuator 21 is disclosed, in which, by providing a hole 28 on a board-like shaped body composed of a piezoelectric/electrostrictive material, a fixing portion 25, movable portion 24, and a beam 26 connecting therewith are integrally formed, and the beam 26 is further provided with an electrode layer 22 (See JP-A-10-136665).
In the actuator 21, when a voltage is applied across the electrode layer 22, the beam 26 expands or contracts, in a direction in which the fixing plate 25 is connected with the movable portion 24, by the inverse piezoelectric effect or the electrostrictive effect, thus enabling the movable portion 24 to have an arc-shaped displacement or a rotational displacement in-plane of the board-like shaped body. On the other hand, JP-A-63-64640 discloses a technique with regard to an actuator utilizing a bimorph, wherein an electrode of the bimorph is split, and by driving the actuator by selecting the split electrodes, precise positioning can be performed at a high speed, and, for example, a structure for using two bimorphs opposed to each other is shown in the specification thereof.
However, in the above-described actuator 21, as the displacement in an expanding or contracting direction (namely, in-plane direction of the board-like shaped body) of a piezoelectric/electrostrictive material is transmitted per se to the movable portion, there is a problem that an operational quantity of the movable portion 24 is small. Moreover, the actuator 21, having all the members thereof being composed of a piezoelectric/electrostrictive material which is fragile and comparatively heavy, has another problem that the actuator 21 per se is heavy and operationally likely to be influenced by harmful vibrations (for example, residual vibrations or noise vibrations when operated at a high speed), in addition to being low in mechanical strength, and inferior in handling, impact resistance, and humidity resistance.
In order to solve the above-described problems in the actuator 21, a proposition has been made that a filler having plasticity is filled in the hole 28. However, when the filler is used, it is apparent that the efficiency of the displacement due to the inverse piezoelectric effect or the electrostrictive effect is reduced.
On the other hand, what is shown in FIG. 4 of JP-A-63-64640 is that, in bonding a relaying member 3 with a bimorph, a portion without a split electrode is joined with the relaying member, and at the joined portion, the effect of the split electrode is unable to be utilized, in other words, merely a bimorph portion which is not a displacement generating portion is joined. Further, a portion where a head is joined with a bimorph is joined in a similar bonding mode. As the result, a bending displacement of the bimorph is developed toward the inner space between the relaying member and the head, and the structure is that an action for effectively displacing the head per se toward the outer space is unable to be obtained. In addition, the actuator disclosed in JP-A-63-64640 is so structured that a displacement generating member and a so-called frame member (relaying member, or the like) are separately prepared, and then adhered to be incorporated, and consequently the structure is that the joined state of the frame with the bimorph is likely to vary with time in accordance with operation of the bimorph, and that drifting of the displacement, exfoliation, or the like is also likely to be caused. Furthermore, a structure having an adhesive agent at a joined portion of the bimorph with the relaying member and at a joined portion of the head with the bimorph, namely at a holding portion of a displacement member, is low in stiffness compared to the holding portion per se, and thus an increase in the resonant frequency which is required in high speed operation is difficult to be obtained.
Of course, the applicant of the present invention and the others have made a proposition of a piezoelectric/electrostrictive device capable of solving such problems in the specification of Japanese Patent Application No. 11-375581, or the like. However, a piezoelectric/electrostrictive device which is capable of further increasing the displacement quantity of a movable portion, and making the displacement path of the movable portion substantially parallel relative to the fixing portion, is sought after specifically as a precise positioning device in the fields of magnetic recording and optics.
The present invention is made in view of the above-described current situation, and an object thereof is to provide a displacement element which is capable of further increasing displacement quantity of the movable portion and making a displacement path of the movable portion substantially in parallel relative to the fixing portion without reducing resonance frequency, and a sensor element capable of detecting vibrations of the movable portion in high precision.
According to the present invention, firstly provided is a piezoelectric/electrostrictive device comprising a driving portion to be driven by a displacement of a piezoelectric/electrostrictive element, a movable portion to be operated based on displacement of the driving portion, and a fixing portion for holding the driving portion and the movable portion, the movable portion being coupled with the fixing portion via the driving portion, and a hole being formed by inner walls of the driving portion, an inner wall of the movable portion, and an inner wall of the fixing portion, and the piezoelectric/electrostrictive device is characterized in that the driving portion comprises a pair of mutually opposing thin plate portions, and a piezoelectric/electrostrictive element including a piezoelectric/electrostrictive operating portion comprising a pair or more of electrodes and a piezoelectric/electrostrictive layer arranged on at least a part of the outer surface of at least one thin plate portion out of the thin plate portions, one end of the piezoelectric/electrostrictive operating portion in a direction in which the fixing portion is connected with the movable portion exists on the fixing portion or the movable portion, and the other end of the piezoelectric/electrostrictive operating portion is arranged on the thin plate portion, and at least one end of the piezoelectric/electrostrictive layer of the piezoelectric/electrostrictive element exists on the fixing portion or the movable portion, and the other end thereof is arranged on the thin plate portion, and the Young""s modulus Y1 of a material composing the thin plate portions and the Young""s modulus Y2 of a material composing a material of the piezoelectric/electrostrictive layer have a relationship that satisfies the following expression, namely;
1 less than Y1/Y2xe2x89xa620.
Here, so long as being within a range satisfying the relationship of the Young""s moduli described above, the movable portion, the thin plate portions, and the fixing portion may be composed of a ceramic or a metal, or respective members may be mutually composed of ceramic materials, or metallic materials, or may be composed as a hybrid by combining the members fabricated with ceramic materials and the members fabricated with metallic materials.
Further provided are a piezoelectric/electrostrictive device characterized in that a movable portion, thin plate portions, and a fixing portion are integrally formed by a ceramic green sheet laminated body being simultaneously sintered, a piezoelectric/electrostrictive device characterized in that a piezoelectric/electrostrictive element has a film-like piezoelectric/electrostrictive element directly formed on the thin plate portion and the movable portion or the fixing portion, and integrally formed by having them sintered, and a piezoelectric/electrostrictive device characterized in that the piezoelectric/electrostrictive layer of the film-like piezoelectric/electrostrictive element does not contain any glass frit.
Further provided are a piezoelectric/electrostrictive device wherein a movable portion displaces so as to satisfy an expression of;
0xc2x0xe2x89xa6xcex8xe2x89xa60.1xc2x0
relative to an angle xcex8 formed by a side of the movable portion, opposing to the fixing portion, in a displaced state and the same side of the movable portion prior to the displacement, a piezoelectric/electrostrictive device characterized in that the length L of a portion arranged on the thin plate portion out of the piezoelectric/electrostrictive operating portion satisfies the following expression, relative to the length e of the thin plate portion and the thickness d of the thin plate portion, namely;
30xe2x89xa6(L/e)xc3x97100xe2x89xa6100xe2x89xa6d/2.5,
and a piezoelectric/electrostrictive device characterized in that, in a virtual circle having the center thereof on a perpendicular dropped from the middle point of a side, opposing to the fixing portion, of the movable portion, in a non-displacement state, to the fixing portion, passing through the middle point of the movable portion in the non-displacement state and the middle point of the movable portion displaced by operation of the driving portion, the movable portion displaces so as to satisfy the following expression of a relationship between the radius r of the virtual circle and the length e of the thin plate portion, the expression being;
0xe2x89xa6e/rxe2x89xa6100,
and when driven by a displacement of the piezoelectric/electrostrictive element, an inflection point of the displacement exists on the thin plate portion.
Further provided in the present invention are a piezoelectric/electrostrictive device characterized in that the length L of the piezoelectric/electrostrictive operating portion arranged on the thin plate portion satisfies the following expression, in relationship with the length e of the thin plate portion and the thickness d of the thin plate portion, the expression being;
40xe2x89xa6(L/e)xc3x97100=100xe2x88x92d/1.5,
a piezoelectric/electrostrictive device characterized in that, in a virtual circle having the center thereof on a perpendicular dropped from the middle point of a side, opposing to the fixing portion, of the movable portion in a non-displacement state, to the fixing portion, and passing through the middle point of the movable portion in the non-displacement state and the middle point of the movable portion displaced by operation of the driving portion, the movable portion displaces such that a relationship between the radius r of the virtual circle and the length e of the thin plate portion satisfies the following expression, the expression being;
0xe2x89xa6e/rxe2x89xa620,
and an inflection point of the displacement of the thin plate portions exists at a position parted more than one half of the length of the thin plate portion from a joined portion of the fixing portion, or the movable portion with the thin plate portion; the piezoelectric/electrostrictive operating portion existing on either portion of the fixing portion, or the movable portion, and a piezoelectric/electrostrictive device characterized in that, relative to the thickness a of the hole and the length e of the thin plate portion, the ratio e/a is 0.1 to 2, and relative to the thickness a of the hole and width b of the thin plate portion, the ratio a/b is 0.05 to 2.
Further, a piezoelectric/electrostrictive device of the present invention preferably has a movable portion, thin plate portions, and a fixing portion, composed of ceramics integrally formed, more preferably have the movable portion, the thin plate portions, and the fixing portion, composed of a material containing fully-stabilized zirconia as the major component, or a material containing partially-stabilized zirconia as the major component, and most preferably have at least the movable portion, the thin plate portions, and the fixing portion, composed by a sintered ceramic green laminated body. The reason is that joined portions with the movable portion, the thin plate portions, and the fixing portion can be structured to be without boundary by being integrated by sintering, thus long term reliability with time of such portions can be raised, a phenomenon such as drifting or the like as variation with time of the device by the displacement can be suppressed to be minimum, and a large displacement can be developed with higher reproducibility. On the other hand, when at least the thin plate portions are composed of a metallic material as described previously, a device superior in the handling property and impact resistance can be provided.
It should be noted that, when fabricating a device of a structure according to the present invention, in addition to the method where all members thereof are integrated by sintering, there is a method in that a laminated body split in a mutually opposing direction of the thin plate portions, namely a ceramic laminated body comprising a thin plate and a member having a rectangular fixing portion and movable portion is prepared, a piezoelectric/electrostrictive element is formed by the screen printing at predetermined positions of the thin plate portion and the fixing portion or the movable portion, and integrally sintered with the ceramic laminated body to prepare at least two of the sintered structures, and the sintered structures are joined together so as to have thin plate portions to be parted from each other, namely to have the above-mentioned members respectively to be a fixing portion and a movable portion mutually matched by use of an adhesive or the like such as glass or an organic resin. However, a device fabricated first by integrating the movable portion, the thin plate portions, and the fixing portion by simultaneous sintering, and then a piezoelectric/electrostrictive element film being formed on the sintered body, and finally by integrally sintering the body thus formed, is preferable as the device has no discontinuous portion as a structure such as a joined portion where the third party intervenes, thus the device thus fabricated is superior in stability and reliability even if a stress is applied thereon by operation of the driving portion, which is preferable.
Moreover, in a piezoelectric/electrostrictive device of the present invention, it is preferable that a piezoelectric/electrostrictive layer constituting a piezoelectric/electrostrictive element is composed of a material containing lead zirconate, lead titanate, and lead magnesium niobate as the major component, and a material containing sodium bismuth titanate as the major component is also preferable. Details of materials to be used are to be described later.
It should be noted that, in the present specification, a terminology xe2x80x9coperate in substantially parallelxe2x80x9d means, with reference to FIG. 26, when both ends of the right-hand side and the left-hand side of the hole at the joined portion of the movable portion with both thin plate portions in a state when the device is not driven are respectively set as the point A and the point B, while positions of the both ends in a state when the device is driven at a predetermined voltage are made as the point C and the point D, a displacement is performed within a range where an angle q to be formed by a segment passing through the point D and parallel to a segment AB and a segment CD satisfies the following expression, namely;
0xc2x0xe2x89xa6xcex8xe2x89xa60.1xc2x0.
For this value, displacement quantities at above-described respective points are measured by the laser Doppler vibrometer (made by Graphtec Corp), and the value is derived by calculating the measured displacement quantities.
In the present invention, xe2x80x9cfilm-likexe2x80x9d means what is formed by the thick film or thin film forming method, as to be described hereinafter, and ordinarily, it is distinguished from the one formed by adhering plate-shaped piezoelectric/electrostrictive elements composed of piezoelectric plates by use of an adhesive. Further, xe2x80x9cpiezoelectric/electrostrictive device (hereinafter simply referred to as xe2x80x9cdevicexe2x80x9d) according to the present specification is a notion implying an element for altematingly converting an electrical energy into a mechanical energy by way of a piezoelectric/electrostrictive material. Accordingly, the device can be preferably used as an active element for a variety of actuators, oscillators, and the like, particularly as a displacement element utilizing a displacement of the inverse piezoelectric effect or the electrostrictive effect, however, it can also be used as a passive element for an acceleration sensor element, an impact sensor element, or the like.
A piezoelectric/electrostrictive element is an element comprising a pair or more of electrodes and a piezoelectric/electrostrictive electrostrictive layer, for being driven based on a signal to be transmitted, and for performing a function of transmitting the movement thereof to the thin plate portions. In the element, a piezoelectric/electrostrictive operating portion is a portion to substantially move the piezoelectric/electrostrictive element so as to move the movable portion in a predetermined operation in accordance with a signal given to said piezoelectric/electrostrictive element, and composed of a portion where a pair or more of electrodes and a piezoelectric/electrostrictive layer are mutually overlapped. It should be noted that xe2x80x9chaving multiple layers of piezoelectric/electrostrictive operating portionsxe2x80x9d means that a plurality of piezoelectric/electrostrictive operating portions are arranged in layers in a direction perpendicular to the main surface of the thin plate portions, namely in the thickness direction of the thin plate portions. Respective electrodes which constitute respective piezoelectric/electrostrictive operating portions may have a structure being shared between operating portions, or a structure made to be in common use, or a structure to be mutually independent. A predetermined signal is transmitted to respective electrodes constituting respective operating portions, and an electric field is applied to a piezoelectric/electrostrictive layer constituting respective operating portions.
Moreover, xe2x80x9cpiezoelectricxe2x80x9d means xe2x80x9cpiezoelectric and/or electrostrictivexe2x80x9d. xe2x80x9cLengthxe2x80x9d means a distance in a direction in which a movable portion is connected with a fixing portion, namely in the Z-axis direction in drawings, xe2x80x9cwidthxe2x80x9d means a distance in a direction penetrating through a hole, namely in the Y-axis direction in drawings, and xe2x80x9cthicknessxe2x80x9d means a distance in a direction in which a piezoelectric/electrostrictive device is laminated with a thin plate portion, namely in the X-axis direction in drawings. It should be noted that in drawings those having the same or similar function is in principle indicated by the same symbol.
Inflection point means a point where the bending direction is changed in a bend of the thin plate portion caused by operation of a piezoelectric/electrostrictive element, and this may be described by use of a piezoelectric/electrostrictive element in the left-hand side in FIG. 2(b) that, in the portion lower than the point indicated as the inflection point, the vertex of the bend is oriented toward a hole, and in the portion upper than the point indicated as the inflection point, the vertex of the bend is oriented toward outside, thus forming a bend, and the boundary is the inflection point. Ordinarily, the inflection point exists in the vicinity of the tip of a piezoelectric operating portion comprising a portion where a pair or more of electrodes and a piezoelectric/electrostrictive layer formed on thin plate portion are mutually overlapped.